In fact, several return lines are affected by the same condition on the KIO3
PCB, including:
L7 - Mic (J20);
L5 - Line In (J21);
L3- Line Out (J22);
L8 - Phones (J19); and
L15 - Speaker (J18).
On the Main DSP PCB, L4 (affecting the front panel Mic jack) is bypassed
with a jumper and removed.
IMHO, the real solution for the KIO3 is to simply disconnect the existing
ring return point on the jacks through a trace cut and bond the jack's ring
terminal to the chassis with a short jumper. The rings should really be
placed at chassis potential as close as possible to the jacks' ring. The
RFCs could be left in place with this option since they would removed from
the circuit anyway.
An alternative option is to remove/bypass the affected RFCs on KIO3 and
jumper the associated CN1-CN3 chip caps (e.g., jumper pins 4 and 5 on CN2
for rear panel mic shell grounding).
Whatever you decide, it's important to refer to the schematic diagrams prior
to making any K3 modification.
Paul, W9AC
----- Original Message -----
From: "hb9brj" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, November 07, 2008 9:46 AM
Subject: Re: [Elecraft] K3 RF Feedback Problem
I had an RF feedback problem when transmitting in digimodes (TX audio via
LINE IN).
On some bands and at power levels above 20W, my TX audio was distorted.
BTW, my previous TRX did not show this problem in the very same setup.
Similar to MIC, also LINE IN has an RFC in its GND line (L5 on the KIO3
Audio IO board).
After removing it and placing a jumper, my problem was gone!
73, Markus
--
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